robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Jun 28, 2016 16:18:49 GMT
Gentlemen I've read this thread twice yet see no mention of the grade of balls used, nor the effects of the coefficient of expansion of O rings. ....... The designs where the O ring forms the seat, whether trapped or contained seem to suffer leaking until there is a significant pressure difference which I suspect is due to deformation as the O ring expands at a faster rate than the valve body. This is likely to cause the O ring to deform because it is trapped in the valve body. GeoffV The thermal expansion point is a red herring. The expansion of a 1/4" dia o-ring at steam temperature is only 2 thou inches in radius, which is negligible. The flexibility of the ring at the joint interface is much greater than this and will compensate for any thermal changes. Rob
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Jun 28, 2016 18:39:00 GMT
So far as lift is concerned it depends on the size of the axlepump and injectors on the loco, injectors allowing a greater amount of lift, though if the check valves on the axlepump are correct then the additional check valve into the boiler can be the same as for injectors.
I think the area around Brian's check valves vis a vis ball diameter and internal body ID is a bit restricted.
I have never had to resort to the use of 'O' rings or the dreaded nitrile balls. I have a set machining sequence and operation for achieving decent seats for the balls. Often a ridge is left if the correct sequence is not used. No amount of burnishing or bashing of balls on seats will cure a poorly machined seat.
I agree you cannot guarantee stainless balls to be of consistent acceptable quality from ME suppliers.
Cheers, Julian
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Post by Roger on Jun 28, 2016 19:24:08 GMT
So far as lift is concerned it depends on the size of the axlepump and injectors on the loco, injectors allowing a greater amount of lift, though if the check valves on the axlepump are correct then the additional check valve into the boiler can be the same as for injectors. I think the area around Brian's check valves vis a vis ball diameter and internal body ID is a bit restricted. I have never had to resort to the use of 'O' rings or the dreaded nitrile balls. I have a set machining sequence and operation for achieving decent seats for the balls. Often a ridge is left if the correct sequence is not used. No amount of burnishing or bashing of balls on seats will cure a poorly machined seat. I agree you cannot guarantee stainless balls to be of consistent acceptable quality from ME suppliers. Cheers, Julian Just to make sure that we're not talking at crosses purposes.... Nitrile balls are like rubber, Silicon Nitride balls are glass hard and a different animal. Whenever I mention Silicon Nitride in a conversation, it's often misunderstood as being Nitrile because that's all most people have heard about and the name is vaguely similar.
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pault
Elder Statesman
Posts: 1,496
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Post by pault on Jun 29, 2016 19:33:31 GMT
It is quite common for people to use nitrile balls in clacks whn they struggle to get them to seal. They often only last a couple of years as nitrile is only rated to about 110 degrees C so is not really suited to the task
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miken
Part of the e-furniture
Posts: 477
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Post by miken on Jun 29, 2016 20:19:49 GMT
It is quite common for people to use nitrile balls in clacks whn they struggle to get them to seal. They often only last a couple of years as nitrile is only rated to about 110 degrees C so is not really suited to the task I'm rather keen on nitrile balls. You get a perfect seal with virtually no effort on a drilled and slightly countersunk hole. They have never given me the slightest problem. I have benn running one of my 5" gauge loco's regularly for nearly 20 years now. I fitted nitrile balls in the 2 injector clacks when i first built it. This last winter I gave the loco a bit of a service and looked inside the clacks for the first time. I put the same balls back in and have run it a few times since. I did replace the nitrile balls in the 2 lubricator in-line non return valves a few years ago. they must have been in there around 13 yrs. I replaced them when I was trying to find a fault which turned out to be with one of the lubricators. I have also fitted a nitrile ball blow down valve to this engine(which gives a very nice finger tight operation) this has been in place for the last 6 years after I had trouble with the stainless ball item that started to leak. I also have them in the double acting hand pump in the above loco tender which I have never looked at since the day I built it and always works when I use it to fill the boiler before a steam up. My boiler testing kit, Butch tank loco, My J tank engine, the bolier feed clacks on my vertical test boiler and the injector clack, crankshaft pump and blowdown valves on my 6" scale traction engine all use them although they dont get such regular use. Im now fitting them to loco that im building at the moment. I only really use s/s balls on safety valves. I burnish these onto their seats by putting a sheet of paper on my surface plate. Place the ball on the paper. Invert the fitting over the ball and do figure 8's for a couple of minutes. This usually does the trick. Cheers Mike
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Jun 29, 2016 21:18:19 GMT
Hi Mike,
Do you use a different shape seat for nitrile balls ie not a 'D' bit type seat? My old friend John Cashmore (of injector fame) hated nitrile balls.
Roger's Silicon Nitride balls are quite excellent and an excellent replacement for the vagaries of stainless balls supplied by our ME suppliers. Sytainless balls - some are not round, and some are the wrong grade and deteriorate/get eaten away/corroded. I have bought many packets of stainless balls from ME suppliers over the years that have been magnetic and get consigned to the bin.
Cheers, Julian
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Post by runner42 on Jun 29, 2016 23:14:26 GMT
Hi Mike,
you are a great believer in Nitrile balls, another aspect to consider, but will Nitrile be something that I can achieve bearing in mind my O ring clack valves didn't operate successfully from 0 - max PSI and required some pressure applied before they sealed?
Your Nitrile ball blowdown valve sounds a good idea. Can you possibly provide some details of how the actuating part acted against the Nitrile ball?
Brian
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Post by sniffipn on Jun 30, 2016 4:22:37 GMT
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Post by sniffipn on Jun 30, 2016 5:14:31 GMT
Roger thanks for the grinding procedure. I selected a USA source on Ebay for the Silicon Nitride balls because I am cautious about using balls that may be not quite the best. I need everything to be spot on so I can achieve a useful clack valve. I hope the USA supplier didn't get the balls from China.
Jim the lift for the ball is 1/32".
Brian I recall buying some skateboard bearings. ABEC 7 was the preferred grade. the eBay Chinese bearings were branded ABEC 7. reasonable quality - certainly adequate for purpose. very competitive price. same product made in china, supplied from USA were a reasonable price. not the same quality as a SKF or Timken bearing though. having written that, the SKF and Timken were several times the cost. in my opinion, the Chinese bearings (including the USA supplied ones) were unlikely to really be ABEC 7. they had the correct branding though. that's what the customer wanted. incidentally both SKF and Timken have factories in china making bearings. big bearings (2000+ mm diameter) for the main shaft in wind turbines. nothing wrong with Chinese product - if its adequately specified and quality controlled. in my experience, the problems come from buyers making unrealistic demands. both buyer (a purchasing professional) and supplier understand market place price. if the buyer drives down the price beyond a sensible level, the supplier makes certain changes (not disclosed unless requested) in the specification, to match/achieve the price. with respect to silicone nitride balls, I appreciate and respect rogers suggestion. I'll order some from china. the uk stockist is most unlikely to have the equipment and skills required to determine specification/quality of the product supplied. in common with most parts factors, they excel at 'moving boxes'. that is, they identify a market demand for product, source product at a competitive price and sell for a good margin (profit). if the customer complains, they wont have the understanding to investigate and address the root cause. they may not have the ability to recognise the iffy quality product in a batch and separate it from the good. their approach is to credit and replace. they have sufficient margin (like apple) and see it as the low cost and manageable approach to meeting customer expectation. in some respects, people may consider it all a bit of a lottery. a lottery for you and me - seeking reasonable quality product, in small quantity, for affordable money.
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
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Post by oldnorton on Jun 30, 2016 10:04:42 GMT
It is good to hear Mike's positive results from several years of Nitrile ball use. I agree that they make good, weep free seatings. However, sometimes a small wisp of steam returning is no great problem. The nitrile ball in my blow down valve was hard and deformed after two years use - but it still sealed and was easy to replace. I have used them successfully in new, in-line clacks; and I have also had a couple of disasters. The big error is to put them in an existing valve where the steel or bronze ball is weeping thinking "that will fix it". It is not just the ball seat that has to be looked at, it is the protection to stop the ball reaching the outlet. A metal ball might be bouncing around the outlet and not quite sealing, so the flow continues. If you put a deformable (nitrile) ball in then it may decide to deform and seal that outlet. If this happens on a hydraulic axle pump line then that nitrile ball will get well and truly stuffed into the fitting and up a length of pipe as a (potential) few thousand psi are exerted. It has happened to me and several others. I now take note to design any valve to fully 'cage' a ball as it lifts off the seat. Gordon Smith reviewed this issue very nicely in EIM January 2015 and showed some good designs. We keep talking about nitrile balls but viton is a higher temperature, fluorocarbon material that is specified for steam seals. I don't understand why nitrile balls keeps getting mentioned, although I think the individual balls are cheaper in nitrile. I am going to persist with 'hard' balls for certain applications and I am now convinced by Roger's advocacy for silicon nitride. The eBay Chinese website makes them easy to obtain at the 5 per million precision www.ebay.co.uk/itm/20pcs-Si3N4-Ceramic-Silicon-Nitride-Si3N4-Bearing-Balls-GRADE-5-G5-0-8-18-256mm-/301633616096?var=&hash=item463ac3b8e0:m:m5dywxQUVdEqprdL9L-VC9AThis link sells 3/32" 20 off for £3.66, the previous link from a UK supplier sells 3/32" 10 off for £33.60 !! The smaller inch sizes (5/32, 3/16, etc.) are not available in smaller quantities so I might buy 20 of each common size and try to sell off surplus numbers to club contacts (Roger will tell us all to be sensible and buy the metric sizes, and I suppose he might be right……) Norm
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miken
Part of the e-furniture
Posts: 477
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Post by miken on Jun 30, 2016 16:53:02 GMT
Brian and Julian, I make the seat for the ball similar to a s/s ball seat, but I just lightly countersink the sharp edge so it doesn't cut the nitrile ball. To arrive at a diameter for the hole I get a piece of scrap flat metal and drill a hole in it. So for a 3/16" dia ball I believe you would normally use a 5/32 or 4mm hole. So drill a hole this size and press the nitrile ball against it with your thumb. You will observe that the ball starts to enter the hole and will not fall out. So try a hole that is a bit smaller, say 3.8mm and you will probably find the same thing happens. when you get to about 3.6 dia you should find that when you release your thumb pressure the ball falls away from the seat. This is your correct diameter. Not very scientific but it has worked for me. The next time I have to buy balls I think I will do as oldnorton suggests and try viton. I have no experience of locomotives fitted with axle pumps I have only ever used injectors (apart from the crankshaft pmp on my T/E). When I started making model steam engines I was told that you shouldn't fit a clack directly to a boiler. I cant remember the reason now but I always try to follow that advice. I usually try to use an in-line type like this one in from my bits box: On a loco I connect it with a short copper pipe and hide it under the footplate in the vertical position feeding the boiler via a dummy clack (an empty elbow) which goes on the boiler. By having a separate screw in ball seat as shown above, I guess it would make it easier to burnish a s/s ball onto the seat using the figure 8 method I described earlier? I have also made close coupled versions like this for my vertical test boiler: Brian , this is the blowdown valve I intend to fit to the loco I am building now.It is a standard Martin evans type : Incidently; I have realised over the years that I never use the hand pumps on my locos except to fill the boiler from empty. So I am no longer bothering to fit them. Instead I just fit an extra slightly larger clack valve and fill the boiler from a hose on a tap. MN
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Post by runner42 on Jul 1, 2016 8:03:02 GMT
Hi Mike,
thanks for the blow down valve info, its something I shall adopt because the current one requires a fair amount of tightening to get it to seal.
Brian
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Post by Roger on Jul 1, 2016 8:41:23 GMT
That's an interesting use of a Nitrile ball for a blowdown valve. I suppose there's no reason why a Ceramic ball couldn't be used for the same purpose.
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oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
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Post by oldnorton on Jul 1, 2016 9:00:05 GMT
Mike,
I like that design for an in-line clack using four drilled holes for the flow route, thank you for showing that. Mine use a castellated nose as a ball-stop with flow, but I think I prefer what you have. I was forced by space constraint to mount one horizontally, but it works fine once steam pressure is there.
Your blow-down is identical in principle to mine. I made the ball just captive so that I can fill the boiler through the blow-down pipe from a small container and electric pump.
Norm
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uuu
Elder Statesman
your message here...
Posts: 2,808
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Post by uuu on Jul 2, 2016 11:13:20 GMT
I've just received a selection of the Chinese balls, from ebay. Took a month to arrive!
I suppose we're interested in roundness, but less concerned that all the balls match!
Wilf
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Post by Roger on Jul 3, 2016 6:28:45 GMT
I've just received a selection of the Chinese balls, from ebay. Took a month to arrive! I suppose we're interested in roundness, but less concerned that all the balls match! Wilf Hi Wilf, You don't say what they're made of. I'd be staggered if there was a measurable difference in Silicon Nitride ones. They usually take weeks to arrived from China, I think they use shipping by Sea to keep the cost down.
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Post by peterseager on Oct 12, 2021 0:24:14 GMT
Mike
Because of problems with my Manor blowdown valves (leaks then ptfe mod gets stuck just like above I searched the board and found you reference to blowdown valves and a photo of the Martin Evans Valve. Unfortunately the photo is removed. I was considering the valve Martin described for the Manor and Fury which is designed around a 1/4" diameter bronze ball. Is this the type that was shown. If not, on what loco did Martin use the one that was shown? You and another contributor were enthusiastic about it.
Looking through postings to try and find the information I was amazed to find your Baltic tank very much like the Modified B1 Baltic Tank I am building,
Peter
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Post by 92220 on Oct 15, 2021 8:22:24 GMT
If Nitrile is not really suitable for use in valves because of it's low temperature rating, why not use Viton balls. I bought a pack of these some time ago but haven't used them yet so have no experience of their suitablility.
Bob.
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robmort
Hi-poster
3.5" Duchess, finishing 2.5" gauge A3 and building 3.5" King
Posts: 172
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Post by robmort on Oct 15, 2021 9:31:20 GMT
Viton balls definitely a good solution, though difficult to find in small sizes and (much) more expension than o-rings, probably because they have to be ground accurately.
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Post by 92220 on Oct 16, 2021 11:53:08 GMT
I must have been lucky then. I bought some 3mm viton balls off ebay last year. I didn't think they were particularly expensive though they were more than nitrile balls.
Bob.
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